The present invention relates to a real image viewfinder which enables observation of an image formed by an objective lens as the objective lens brings the object into focus and indicates that the object is in focus, and particularly to a real image viewfinder which forms an erect image of the object in a field of view through an observation pupil.
The invention is especially suitable for use in a camera for viewfinding purposes. The invention may also be used in optical sighting devices for other purposes.
Viewfinders which have been proposed utilize a Type II Porro prism having a pattern or reticle, sometimes called a field frame, which is etched on a surface of the prism. A Porro prism is a well known optical device having totally reflecting right angle prisms which inverts and reverts the image and increases the optical path without increasing the length of the viewfinder. It is sometimes desirable to avoid using a Porro prism, especially where it is desired to reduce the costs of the viewfinder. Etching the finder pattern (reticle) on the prism surface also increases the cost of making the viewfinder.